Chlorinated polyvinyl chloride resin (CPVC) is a thermoplastic polymer that can be produced by post-chlorinating polyvinyl chloride resin (PVC). It can be processed and formed into various useful articles by conventional techniques, such as milling, calendering, extruding, laminating, compression molding, transfer molding, and the like.
The post-chlorination of polyvinyl chloride resin has been accomplished commercially by forming a suspension of finely-divided PVC particles in an aqueous medium, saturating the aqueous medium with chlorine gas (usually at a temperature no greater than about 65.degree. C.), and, then, photo-illuminating the suspension, with agitation, with a constant source of illumination to induce the chlorination reaction between the dissolved chlorine and suspended PVC particles in the suspension. Additional chlorine gas is fed into the suspension to insure that an excess amount of dissolved chlorine gas always is present in the suspension. The chlorination reaction is terminated when the desired degree of chlorination is achieved by discontinuing the photo-illumination of the suspension. Such a process for chlorinating PVC resin particles is described in U.S. Pat. No. 2,996,489 to Dannis and Ramp, the disclosure thereof being incorporated herein by reference.
U.S. Pat. No. 3,100,762 to Shockney, the disclosure thereof being incorporated herein by reference, discloses that a faster chlorination can be realized by conducting the chlorination at elevated temperatures and pressures in the presence of a swelling agent, but in the absence of photo-illumination. It is taught therein that no catalyst and, particularly, no photo-illumination is required when chlorination is accomplished using a temperature within the range from about 60.degree. C. to about 100.degree. C. and a reactor pressure within the range from about 20 to about 80 psig, if oxygen is substantially excluded from the reactor. It further teaches that inferior chlorinated products are obtained under the aforementioned reaction conditions if the chloromethane swelling agent is omitted from the reaction mixture.
Additional efforts to improve the above-mentioned processes for the chlorination of polyvinyl chloride resin have been made. U.S. Pat. No. 3,506,637, the disclosure thereof being incorporated herein by reference, teaches the use of a specially prepared PVC which is chlorinated in the presence of a controlled supply of oxygen in the absence of swelling agents. As disclosed in U.S. Pat. No. 3,632,848, the disclosure thereof being incorporated herein by reference, the rate of thermal chlorination of an aqueous suspension of PVC is improved when chlorination is initiated at or above 100.degree. C. and below 140.degree. C. while the suspension of PVC is purged with nitrogen to remove oxygen. A process similar to that disclosed in U.S. Pat. No. 2,996,489 is described in U.S. Pat. No. 3,167,535, the disclosure thereof being incorporated herein by reference, with the exception that a catalytic amount of a reducing agent (such as aliphatic and aromatic aldehydes, reducing sugars and alkali metal sulfides) is included in the chlorination reaction. U.S. Pat. No. 3,334,078, the disclosure thereof being incorporated herein by reference, teaches that the addition of a small amount of a colloidal silica or colloidal mineral silicate to the suspension of PVC resin in the aqueous medium containing a chlorohydrocarbon swelling agent prior to the chlorination results in an improved process and a product of improved quality as compared to that resulting when the colloidal silica or mineral silicate is absent. U.S. Pat. No. 3,334,077, the disclosure thereof being incorporated herein by reference, discloses that the addition of a small amount of acrylic acid polymer to the suspension of PVC resin in the aqueous medium containing a chlorohydrocarbon swelling agent prior to the chlorination also is beneficial. It also is known that the chlorination rate can be increased by adding to the PVC/aqueous medium suspension a catalytic amount of a free radical-producing agent, such as, for example, azo compounds, peroxy compounds, peroxides, nitroso compounds, redox catalysts, and the like.
In the copending application of Alan James Olson and Robert Gerard Vielhaber, Ser. No. 350,982, filed Feb. 2, 1982, now U.S. Pat. No. 4,412,898, it is taught that PVC resin in an aqueous suspension can be chlorinated in the absence of any catalyst other than UV light, without the use of swelling agents for the PVC, by initiating chlorination at or below the Tg of the PVC, but preferably above 60.degree. C., and at a pressure above about 15 psig, provided that the reactor is substantially free of molecular oxygen.
As indicated above, it has been the practice commercially to accomplish the chlorination of the PVC resin by exposing the PVC/aqueous suspension to photo-illumination from a constant source of illumination until the desired degree of chlorination is achieved. Various sources of constant illumination have been used, such as ordinary incandescent lamps, mercury vapor or arc lamps, neon glow tubes, carbon arcs and sodium vapor lamps. Commercially, mercury arc lamps generally have been used to initiate the chlorination reaction of PVC. However, when using mercury arc lamps, the amount of UV radiation developed is difficult to control. Further, a mercury arc lamp produces discrete wavelength emmissions of about 253, 310 and 360 nanometers which limits the flexibility of the chlorination. Thus, improvements in the process of post-chlorination of PVC resin still are being sought.